Relief scheme bids to avoid ’09 flooding repeat

Fourteen properties on the outskirts of Ennis were either surrounded or flooded by high levels of flood-waters during unprecedented flooding in November 2009, a new report has revealed.
Clare County Council-appointed consultants Ryan Hanley stated in a new planning report the November 2009 flooding event saw the most dramatic flooding of recent history with the Ballybeg stream backing up and inundating large areas of agricultural land and private properties.

Two properties were flooded and another 12 dwellings saw flood-waters reaching their driveway and footpath surrounding their houses.

The Ballybeg swallow hole has limited capacity, which may have deteriorated in recent years, resulting in flood levels surcharging upstream of it and inundating surrounding properties and roads.

Extreme flooding has occurred in this area during the 1995, 1999 and November 2009 flood events. The nature of the system is such that flooding can prevail for many weeks with roads and house entrances cut off.

The proposed works will divert flood-waters over an overflow weir to a dedicated flood overflow culvert, which will convey the flood-waters from the Ballybeg Stream to the culvert under the N85, which drains to the Clare Abbey floodplain.

The flood overflow culvert will only come into operation once the water level at the swallow hole reaches a height of 3.2m and therefore will not have any effect on the existing hydrogeological regime of the catchment.

In a planning report prepared for An Bord Pleanála seeking its approval to carry out flood-relief works located in the townlands of Clonroadmore, Ballybeg and Clareabbey, the consultants noted during the period of November 18 to 21, 2009, the flood water level overtopped the Limerick Road wall, cascading over it and crossed the Limerick Road, flowing downhill through the Ard Aoibhinn housing estate.

From Ard Aoibhinn, flood-waters flowed through properties to reach the Tobertaiscain Stream. The flood-waters entered the Clare Abbey floodplain due to the combination of high inflow from the Ballybeg and St Flannan’s streams and high flood levels in the Fergus Lower, posing a severe risk to the existing low lying housing and industrial estates between Quin Road and Clare Abbey.

This flooding, which was reported to be the worst in living memory, forced St Flannan’s to close for several days in addition to flooding or cutting off access to a number of homes in the Ard Aoibhinn and Honeywell estates and Toberteascain and St Flannan’s Drive areas.

Important town access roads in the area were impassable and an electricity supply substation at the college had to be switched off as a precaution due to the high flood levels.

St Flannan’s Stream, which has a catchment of less than 5km2, upstream of the college, drains to a sink or swallow hole at the edge of the college sports field. The swallow hole has proven to be connected to springs located 880m east at Toberteascain via an underground karst conduit system.

When the capacity of this underground system is exceeded, St Flannan’s Stream backs up and begins to flood the lands in the vicinity of the swallow hole. Flooding around the swallow hole at St Flannan’s is reported to be a regular occurrence, following prolonged wet spells and generally in winter when groundwater levels are high.

The provision of a new flood overflow culvert will divert flood-waters from the swallow hole at St Flannan’s Stream over an overflow weir to a dedicated overflow culvert, which will cross St Flannan’s grounds and follow St Flannan’s Drive, across the Limerick Road and down Toberteascain Road to the Clare Abbey floodplain where it will discharge to the existing backdrain channels.

Meanwhile, a Natural Impact Statement (NIS) has been prepared by the consultants as part of the application for approval in respect of the proposed development.

Submissions and observations in respect of the proposed development relating to the implications of the proposed development for proper planning and sustainable development in the area concerned.

The likely effects on the environment of the proposed development and its effects on a European site can be made to the appeals’ board before 5.30pm on October 23.

A copy of the NIS, and the documents, particulars, plans, and other information relating to the application, may be inspected at Clare County Council or Ennis Town Council offices.